The difference between finished flaps and unfinished flaps has been known to be that finished flaps contain a folded closing edge, while unfinished flaps have an unfolded, open and consequently unfinished closing edge tending to fray. This difference also requires different sewing-on processes. Thus, finished flaps are always sewn on the fabric part, which may be a shirt part, a pants part or a jacket or coat part, in an aligned position that always corresponds to the later position of use. In contrast, unfinished flaps are first positioned in an aligned position that is rotated by 180.degree. relative to the later position of use, then fastened to the fabric part with a first seam located close to the unfinished closing edge, then they are folded over this seam into the position of use, and finally sewn on the fabric part with a second seam. The process for sewing on unfinished flaps has been known from, e.g., the PFAFF information brochure "PFAFF Special Service 310-01," printed March 1983.
A process for sewing a finished flap and a pocket on a fabric part, in which the flap is positioned on the fabric part in relation to the pocket such that it first assumes a nonoverlapping position, has been known from DE 41 24 164 C2. These three workpiece parts are grasped by a fabric holder and fed together to the sewing machine by means of a support plate of the sewing unit. Then, the pocket is first sewn on the fabric part. The fabric part with the sewn-on pocket is then fixed on the support plate by means of an additional, stationary holding means operated with suction air. The flap is fixed during this time at a flap-clamping plate either by a suction air holding means or by means of a mechanically acting gripping holding means, the entire fabric holder together with the flap-clamping plate and the flap-holding means is pushed off from the fabric part and the pocket and then displaced horizontally to the extent that the flap will overlap the pocket in the desired manner. After the fabric holder has been again lowered onto the fabric part and the pocket, the flap is sewn on the fabric part in its position of use.
Due to the measure of transferring the flap from a first into a second position after sewing on the pocket, the normal holding function of the fabric holder, i.e., the clamping function in cooperation with the support plate, must be eliminated during this process step. Since the holding function for the workpiece parts to be displaced in relation to one another must be assumed, instead, by two additional holding means, the means for carrying out this process are comparatively complicated. Furthermore, there is a risk that the relative position of the flap in relation to the pocket or to the position of the programmed flap seam to be sewn subsequently will be displaced during the transition of the holding function from the fabric holder to the two additional holding means and vice versa. Since the flap seam is located at a short distance from the upper edge of the flap only, such a displacement or even a rotation by a certain angle would lead to a sewing result of an unattractive appearance.
A process and a sewing unit for sewing on an unfinished flap, in which process and sewing unit the flap is placed on a fabric holder in a position rotated by 180.degree. in relation to the later position of use, have been known from DE 197 05 314 A1. The fabric holder takes over the folded pocket in the known manner and feeds the fabric part, the pocket and the flap to the sewing machine, where the pocket is sewn on first. The fabric holder is subsequently moved to a stationary holding means (98), which holds the fabric part together with the sewn-on pocket and the still loose flap on the support plate by means of suction air. The fabric holder is raised during this time and is displaced in the horizontal direction from the pocket sew-on position into the flap sew-on position. A holding strip (80) comes to lie on the edge of the flap in the vicinity of the seam to be prepared first during the lowering of the fabric holder and it subsequently holds same. As soon as the first flap seam has been formed, the flap is folded around the seam or the holding strip (80) into its position of use by means of a turning strip (66) and is held in this position, after which the second flap seam is formed.
Another sewing unit, which is used to sew on unfinished flaps, has been known from DE 197 15 340 A1. For the functions of holding and folding over the flap, this sewing unit has a total of three components arranged on a fabric holder (40), namely, a flap clamp (53), a holding strip (77), and a turning strip (74) called a clamp turner. The process of sewing on the flap is essentially the same as in the sewing unit according to the above-mentioned DE 197 05 314 A1, but with the difference that during folding over into the position of use, the flap is folded around the first flap seam as in the case of the process carried out manually according to the above-mentioned PFAFF brochure, rather than around the holding strip. After sewing on the pocket, the fabric holder is moved to a stationary holding means (93) in this sewing unit as well, and the holding means (93) will then hold the fabric part together with the sewn-on pocket on the support plate of the sewing unit by suction air. The fabric holder is then lifted off from the fabric part and the pocket and is displaced by a predetermined path in the horizontal direction and is then again placed on the fabric part and the pocket, after which the flap is now in its correct position in relation to the pocket.
Thus, the two prior-art sewing units for sewing on an unfinished flap have one essential feature in common, namely, that the normal holding function of the fabric holder, i.e., the clamping function in cooperation with the support plate, is eliminated after sewing on the pocket, in order to be able to displace the fabric holder at least in relation to the fabric part and the sewn-on pocket. Therefore, there is also a feature in common with the sewing unit known from DE 41 24 164 C2 for sewing on finished flaps, i.e., the two sewing units for sewing on unfinished flaps have the same basic drawbacks, namely, the complicated means, on the one hand, and, on the other hand, the risk that the relative position of the flap in relation to the sewn-on pocket may be displaced.